The paint is dry, which means that assembly of the Buick 401 Nailhead can finally begin. It’ll be easy—just put it back together, right? Not so fast. There’s a proper way to assemble a set of Buick cylinder heads and Davin is here to talk us through the details.

The Buick Nailhead has odd cylinder heads when compared to a small-block Chevrolet or Ford. The quirks of the Buick Nailhead lie mainly in the angle of the valvetrain. Contrary to other cylinder heads that get the spring seats cut at the machine shop, the Buick’s heads would end up in the scrap heap if its seats were skimmed by a cutter. Because the seat is so close to the hole for the pushrods to travel though, removing any material would shrink the seat and create an uneven surface.

So, with this engine, it’s extra important to check spring heights during assembly. Davin outlines the process in the latest episode of Redline Update, leading up to the final Redline Rebuild of the Nailhead coming up soon. Using the valves, retainers, and keepers that will be used in the final assembly, Davin replaces the spring with a special micrometer that can measure the size of shim required to achieve appropriate spring height and pressure. Only once the shims are determined for each valve—and yes, it is important to measure each valve and not just one—the final assembly can begin.

With a set of complete cylinder heads sitting on the table, Davin now has to turn his attention to getting a short-block ready to receive them. Once installed, the rocker shafts will be placed and, finally, adjusted. Though he makes it look easy, this attention to detail is painstaking, a degree of obsession essential to a machine as finely-tuned as an engine. It’s just a few more days until we get to hear the engine fire up and witness the payoff of all this hard work.

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